Conventionally, a thermoplastic resin film is drawn to express an in-plane retardation (Re) and a thickness-direction retardation (Rth) and used as a phase contrast film for a liquid crystal display device to enlarge a viewing angle.
As methods of drawing such a thermoplastic resin film, known are a method of drawing a film in the longitudinal (length) direction (longitudinal drawing), a method of drawing a film in the transverse (width) direction (transverse drawing) and a method of drawing a film simultaneously in the longitudinal and transverse directions (simultaneous drawing). Of them, the longitudinal drawing has been frequently employed since it can be performed in compact equipment. The longitudinal drawing is generally performed by drawing a film between not less than two pairs of nip rollers while heating it to a glass transition temperature (Tg) or more, and rotating the pair of nip rollers arranged near the outlet faster than that near the inlet.
Japanese Patent Application Laid-Open No. 2002-311240 describes a method of drawing a cellulose ester film longitudinally. The method described in the patent document (No. 2002-311240) is intended to improve variation in the angle of a delayed axis by drawing the film longitudinally in the reverse direction to the casting direction thereof. Japanese Patent Application Laid-Open No. 2003-315551 also describes a drawing method by providing nip rolls, which are arranged in a short span (distance) having a length/width ratio (L/W) of 0.3 to 2 (both inclusive), in a drawing zone. According to the patent document (No. 2003-315551), the thickness-direction retardation (Rth) is improved. The length/width ratio (L/W) used herein refers to a value obtained by dividing the distance (L) between nip rollers for use in drawing by the width (W) of a thermoplastic resin film to be drawn.